The present invention relates to an electrical plug. More particularly this invention concerns such a plug adapted to be secured by a retaining collar to another plug or socket.
An electrical connector assembly as defined in U.S. Pat. No. 5,376,015 and used for a proximity switch has a threaded part having a conductor, an unthreaded part having a conductor, fittable along an axis with the threaded part for engagement of the conductors with each other, and formed with front and back axially spaced stops, and an internally threaded nut axially displaceable on the unthreaded part between the stops through a predetermined axial distance, rotatable about the axis on the unthreaded part, and threadedly engageable with the threaded part to lock the parts axially together with the nut engaging the front stop. The nut is formed with at least one axially extending and radially projecting tooth, the unthreaded part is formed with at least one axially extending and radially projecting tooth, and the teeth are so positioned that they come into engagement with each other only during a small fraction of the displacement of the nut on the unthreaded part immediately prior to engagement with the front stop.
Thus with this system in the last stages of securing the two parts together, as the nut is given its last turn or two, the teeth engage each other and increase the resistance to relative rotation between the nut and the threaded part. When the parts are initially threaded together and during the initial stages of screwing down the nut, the teeth are not in radial engagement with each other and may not even be in angular engagement with each other. Once they are engaged with each other, any force tending to unscrew the nut will have to make the teeth pass each other. Thus such a connector assembly is unlikely to open up as the result of vibration causing the nut to unscrew, since in the initial stages of such unscrewing the teeth must be deformed to allow the two parts to rotate relative to each other.
The disadvantage of this system is that, with time, the teeth wear. They can eventually become so worn down that they scarcely touch, offering no significant resistance to unscrewing of the nut.
It is therefore an object of the present invention to provide an improved electrical plug.
Another object is the provision of such an improved electrical plug which overcomes the above-given disadvantages, that is which will have a long service life so as, even when quite old, to effectively resist unscrewing.
An electrical connector has according to the invention an insulating body centered on an axis, carrying at least one conductor, and having a radially outwardly directed tooth having a radially outwardly directed outer surface with an apex spaced at a predetermined radial distance from the axis. A nut rotatable about the axis on the body bears axially forward on the body and has a radially directed tooth axially level with the body tooth and having a radially inwardly directed inner surface with an apex forming on rotation of the nut about the body an orbit having a radius from the axis greater by a predetermined spacing than the predetermined radial distance of the body-tooth outer-surface apex. A radially compressible ring surrounding the body overlies the tooth outer surface. The ring has a cross-sectional diameter equal to more than the predetermined spacing between the nut tooth and the body tooth so that for the nut tooth to angularly pass the body tooth it must compress the ring to the predetermined spacing.
Thus with this system actual engagement of the teeth with each other is avoided; instead they compress the ring that comes between them. This ring can be made of a highly durable and compressible material so that it will have a long service life. Even if it wears out, it can be replaced easily. It is normally an O-ring.
According to the invention offset from the inner-tooth outer-surface apex the nut has a radial dimension which is generally equal to the radial distance of the body-tooth outer-surface apex plus the cross-sectional diameter of the ring. Thus except when the teeth are angularly passing each other, the ring is substantially uncompressed.
The body according to the invention is formed with a groove receiving the ring and having a floor from which the body tooth projects. In addition the body is formed with a plurality of the body teeth angularly equispaced about the axis and the nut is also formed with a plurality of the nut angularly equispaced about the axis. The nut teeth are more numerous than the body teeth, normally twice as many. There are at least three body teeth and the body is of round-cornered polygonal section at the body teeth. In a particularly advantageous system giving eight stable positions for the nut there are four body teeth and the body is of generally square section at the body teeth.
The nut has a radially inwardly directed rim formed with the nut tooth and the body has a radially outwardly directed annular ridge against which the rim can bear axially forward. More particularly the body has a pair of axially confronting stop faces between which the rim is captured and spaced apart by an axial distance equal to substantially more than an axial thickness of the rim. The rim is movable between a forward position with the teeth axially level with each other and the rim bearing on one of the body faces and a rear position with the teeth axially offset from each other and the rim bearing on the other of the body faces.